Sperm maturation occurs in the proximal epididymis if locally produced dihydrotestosterone is available to stimulate secretion by the epithelial cells. Maintenance of the enzyme 5 alpha-reductase necessary to produce dihydrotestosterone may be dependent on continuous availability of component(s) in rete testis fluid. In preparation for testing the hypothesis that a factor(s) in rete testis fluid controls activity of epididymal 5 alpha-reductase and epididymal secretion and hence sperm maturation, we have developed a procedure to isolate viable principal cells from the epididymal epithelium and have available ample quantities of rete testis fluid. Two potential control points for contraceptive action will be examined by proposed studies aimed at (a) identification of the regulatory component(s) in rete testis fluid and (b) establishment of factors controlling the nature of epididymal secretions The role of rete testis fluid in controlling epididymal function will be studied using highly purified preparations of principal cells isolated from several regions of the rat epididymis. Absorption by principal cells of 3H-protein will be studied radioautographically. Activity of 5 alpha-reductase will be measured in principal cells cultured in native rete testis fluid or semipurified components or rete testis fluid. Regional differences in secreted protein and the role of hormonal milieu on characteristics of secreted protein will be established. Principal cells will be cultured in medium containing 3H-amino acids and 3H-proteins release into the medium will be characterized by immunologic and electrophoretic techniques. Success in manipulating either control point for epididymal function could allow inhibition of sperm maturation and reversable contraception.